Telephone users require an increasing number of features and functions in their telephone systems. With the proliferation of home security systems, it is also desirable to protect a telephone system as well as the doors and windows in the home. Telephone lines are normally powered by an outside power source. Usually, there is no indication that the telephone line has been severed unless someone picks up a telephone set and notices there is no dial tone. Similarly, for telephone systems incorporating telephone answering devices (TAD's ) or other features that require a power source, there generally is no indication that power to the unit has been lost, other than the loss of lights on the unit.
Another problem that conventional telephone systems face is a telephone set that has been left off hook. This is a common occurrence which creates a great deal of frustration for an outside caller. While the telephone operator may be contacted to verify an off hook condition, a telephone user currently has no indication other than picking up a telephone set that a telephone set in another room has been left off hook.
Another problem that telephone systems face is telephone call screening capability. A TAD is often used to screen undesirable calls such as calls from solicitors or calls received at inconvenient times. However, the screening process requires the user to listen to messages left on the TAD, and does not solve the problem where a desired call may result in a hang up the moment the caller is connected to the TAD. A telephone system that provides an improved telephone call screening capability would be very useful and is greatly needed.